1. Field of the Invention
The present invention relates generally to the field of magnetic recording and more particularly to magnetic heads for perpendicular recording.
2. Description of the Prior Art
Perpendicular magnetic recording is a recording technique in which magnetic data bits on a magnetic recording disk are defined such that their magnetic moments are perpendicular to the plane of the magnetic recording disk, as opposed to in the plane of the disk as occurs with longitudinal magnetic recording. The progress to perpendicular recording from longitudinal recording is seen as one of the advances that will allow the continued increase in data densities on magnetic recording disks in the coming years.
A recording head comprises a transducer 100, and a slider 101 (only a portion of which is shown in the various figures so that their scale might allow a clear depiction of the transducer structure). FIG. 1 shows a cross-sectional view of a transducer 100 according to the prior art. The transducer 100 comprises a perpendicular recording write element 105 and a read element 110 that both terminate at a terminus surface (TS). The terminus surface of the transducer 100 is approximately parallel to an air bearing surface (ABS) of a slider 101 and can be either coplanar with the ABS or slightly offset therefrom, usually with a slight amount of recession. The read element 110 includes two shields 115 and a magnetoresistive (MR) stripe 120.
The perpendicular recording write element 105 includes a bottom pole 125, a writer pole 130, a top shield 135, and a shield pedestal 140. The bottom and writer poles 125 and 130 are joined together to form a first yoke. The first yoke includes coil windings 145 disposed between the bottom and writer poles 125 and 130. The writer pole 130, top shield 135, and shield pedestal 140 are also joined together to form a second yoke, and the second yoke also includes coil windings 150 disposed between the writer pole 130 and the top shield 135. Additionally, the second yoke further includes a gap layer 155 disposed between the writer pole 130 and the top shield pedestal 140 in the vicinity of the terminus surface. Also shown in FIG. 1 are a number of encapsulating layers 157, formed typically of a dielectric material such as alumina (Al2O3).
Of particular concern to the performance of the write element 105 is a throat height (TH) of the shield pedestal 140. The throat height is defined as a distance between the terminus surface and a back edge 160 of the shield pedestal 140. The throat height, as well as a depth of the MR stripe 120 as measured from the terminus surface (i.e., the stripe height, SH), are commonly defined by a lapping process that forms the terminus surface. To better appreciate the difficulty in controlling the throat height during the lapping process it is useful to understand the overall fabrication process.
Fabrication of the transducer 100 is typically performed in a batch process in which multiple recording heads, each including a transducer 100, are formed on a wafer and then cut apart. Starting with the bare wafer, multiple patterned layers of magnetic, electrically conductive, and dielectric materials are deposited through well known deposition and planarization techniques to provide rows of unfinished perpendicular recording heads. After the deposition steps have been completed, the transducers of these unfinished perpendicular recording heads resemble the transducer 100 of FIG. 1 except that the terminus surface has not yet been defined and the layers that will be exposed at the terminus surface extend beyond where the terminus surface will ultimately be defined (to the left of the TS in FIG. 1).
Next, rows (sometimes referred to as slider bars) of unfinished perpendicular recording heads are cut from the wafer. The cutting process produces a face on each bar that is then polished back to form the terminus surface. The polishing process is typically a lapping process, and during the lapping process the layers that will be exposed at the terminus surface are also polished back. The importance of accurately determining when to stop lapping will be apparent, as this determines the position of the terminus surface and the critical dimensions of the throat height and stripe height. Overlapping, for example, can completely remove the MR stripe 120.
It will also be understood that the face that is lapped to form the terminus surface has two dimensions, a longitudinal direction that extends perpendicular to the plane of the drawing in FIG. 1 and a transverse direction that extends from top to bottom in the plane of the drawing. Multiple unfinished perpendicular recording heads extend along the bar in the longitudinal direction. In the prior art, considerable attention has been directed to controlling the lapping process in the longitudinal direction so that the transducer 100 on each of the unfinished perpendicular recording heads on the bar are lapped to approximately the same degree. Absent such control, many transducers are either overlapped or underlapped.
Controlling the lapping process in the longitudinal direction is typically achieved through the use of electric lapping guides (ELGS) that are placed in multiple locations on the bar, for example, at both ends and the center. An ELG is commonly a metal layer between two electrical contacts that is exposed at the face and lapped concurrently with the rest of the bar. In some instances the MR stripe 120 can be used as an ELG. Lapping the ELG causes the electrical resistance measured between the two contacts to increase. Lapping can be controlled in the longitudinal direction, therefore, by monitoring the ELGs along a bar and adjusting the pressure being applied to the bar at different locations along its length. In this way each transducer 100 along the length of the bar is lapped at approximately the same rate. Lapping is terminated when the resistance measured across some or all of the ELGs exceeds some threshold.
FIG. 2 shows a cross-sectional view of the transducer 100 of FIG. 1 and illustrates the effect of not controlling tilt in the transverse direction during lapping. A dashed line in FIG. 2 indicates the position of the TS from the example of FIG. 1, and TS′ is the terminus surface defined through lapping without controlling transverse tilt. As can be seen from FIG. 2, when lapping is controlled by the resistance of the MR stripe 120, or by an ELG disposed near the MR stripe 120, a very slight tilt of the bar with respect to the transverse direction can seriously overlap or underlap the shield pedestal 140. Comparing FIGS. 1 and 2, the stripe height is essentially the same in both examples, however the throat height in FIG. 2 is approximately half of the throat height in FIG. 1. It has been found, for instance, that a mere 1° tilt in the transverse direction can translate into a 0.15μ difference in the throat height.
Therefore, what is needed is a way to better control the throat height when lapping to form a terminus surface of a transducer.